Flow control system for loadhandling apparatus



July 27, 1965 W. L- CHICHESTER FLOW CONTROL SYSTEM FOR LOAD-HANDLINGAPPARATUS Filed Dec. 14, 1962 FIG. I

2 Sheets-Sheet 1 INVENTOR WILLARD L. CHICHESTER ATTORN EY July 27, 1965W. L. CHICHESTER FLOW CONTROL SYSTEM FOR LOAD-HANDLING APPARATUS FiledDec. 14, 1962 2 Sheets-Sheet 2 WILLARD L. CHICHESTER f5 (UM ATTORNEYUnited States Patent 3,i%,755 FLQW CGNTRGL FER LUAD- HANDLKNG APPARATUSWillard L. Chichester, Battle Creek, Mich, assignor to t'jlarh EquipmentCompany, a corporation of Michigan Filed Dec. 14, 1962, Ser. No. 244,8237 Claims. (ill. 91-4l1) This invention relates to a flow control systemfor loadhandling vehicles, such as lift trucks, and more particularly toan improved valve construction for use in such a system. It isparticularly Well-suited for use in indusrial lift trucks having a pairof cylinders for tilting the truck mast.

When a lift truck is turned, such as when rounding a corner, the load onthe fork tends to twist the mast. The two tilt cylinders, which controlthe position of the mast, permit such twisting when the cylinders areconnected to one another, because the fluid from one cylinder can crossover to the other cylinder. That is to say, fluid from the heavilyloaded cylinder can flow over to the lightly loaded cylinder. This isundesirable because of resulting undue strain on the mast and can beunsafe because at times the mast tends to sway dan erously.

My flow control system utilizes an improved tilt lock control valve forthe tilt cylinders of lift trucks, for example, which are connectedbetween the truck body and the mast of the truck for pivoting theupright forwardly and rearwardly of a vertical position whereby to aidin picking up loads (forward tilt) and in carrying loads (backwardtilt). During tilting operation it is important that both the head androd ends of the tilt cylinders be maintained full of hydraulic fluid,preferably at a positive pressure, so that no cavitation can occur inthe cylinder and so that the pistons are positively locked in any givenselected pivoted position of the mast. Olson et al. US. Patent No.3,022,773 discloses one means which purports to accomplish this result.

My invention provides improved fluid locking valve means in flow controlsystems of the type contemplated, and it is a main object of the presentinvention to provide in certain types of load-handling apparatus animproved valve construction for preventing crossover of fluid betweencylinders in the system after actuation thereof to predeterminedpositions, and which valve means also permits the cylinders to beconnected together for receiving fluid from a common source.

A further object of the invention is to provide in a fluid controlsystem of the type contemplated improved valve means preventingcross-over between cylinders of the system under certain conditionswhile providing for the supply of pressure fluid to the cylinders from acommon source, and also being adapted to positively prevent cavitationin any of the cylinders under certain conditions of operation.

Another object of the invention is to provide in a fluid control systemof the type contemplated improved valve means providing a positive sealbetween conduits connecting a pair of oppositely disposed cylindersunder certain 'ice embodiment of my improved valve means which forms apart of the hydraulic circuit illustrated in FIG. 2; and

FIGURE 4 is a cross-sectional view of a modified form of the valve meansshown in FIG. 3.

Referring now to the drawings, and particularly to FIGS. 1-3, the lifttruck 14? has a mast 12 at its front end pivoted from the front driveaxle of the truck for tilting movement from a rearwardly inclinedposition, to a slightly forwardly inclined position as shown in dottedlines. A fork carriage 14 is elevatable on mast 12 by conventionalhydraulic hoist and chain means, not shown. A pair of tilt cylinders 16and 18 have pistons 20 and 22 which are pivotally connected by pistonrpds Z4 and 26 and suitable bracket and pin means to mast 12, the headends of the cylinders being pivotally connected by bracket and pin meansto the body of the truck.

Hydraulic fluid is supplied to and exhausted from the cylinders by theoperation of a tilt-lock valve shown generall at numeral 35) and amanually operated directional control valve $2, the latter valve beingsupplied with hydraulic fluid under pressure from a pump 34 through alinefiti. The directional control valve i a three-position,four-connection valve having a closed center. However, when thedirectional control valve is in its closed position, as illustrated,there is a return line 38 from the pressure line so to a sump Thedirectional control valve is actually a spool valve and the symbolsshown merely simplify the disclosure of the spool valve.

When valve 32 is shifted to the left, parallel channels 32 thereinconnect with lines 36 and 44 and with lines 33 and 46 so that fluidunder pressure is supplied from line 36 to line 54 and fluid isdelivered from line $6 to the sump til. When the directional controlvalve is shifted to the right, reversing channels 48 cause fluid underpressure to be delivered from line 36 to line 46, and enable fluid to bedischarged from line 44 to the sump by way of line 33. Lines 59 and 52connect the head ends of cylinders 16 and 18 to positions of tilt-lockvalve 35 and are connectible upon manipulation of control valve 32 toeither pump 34 or sump 463, whereas lines 5d and 56 connect the rod endsof cylinders 16 and 18 to other portions of valve 319 and arelikewiseconnectible by manipulation of control valve 32 to either the pump orsump, as will be described in detail below.

Abody 6d of control valve 39 is formed to provide a plurality oftransversely spaced ports comprising a first pair of ports 62 and 64which are connected to the head ends of the cylinders by lines 5t and52, respectively, a second pair of spaced ports 66 and 68 which areconnected to the rod ends of the cylinders by lines 54 and 56,

respectively, a, single transversely disposed port 70 which is connectedto line 44, and a pair of longitudinally spaced ports 2 and 74 Which areconnected to line 46 and open to the atmosphere, respectively. Ports 62and 64 are connected to each other by a transverse passage 76, whichpassage also communicates with port '72 and intersects a longitudinallyextending valve bore 78 which opens into port 74. Valve bore 78 isformed of three portions of different diameters, viz, a large diametervalve" chamber portion 8t an intermediate diameter portion 82, and asmall diameter portion 84, said portions 80 and 82 forming in the planeof intersection thereof an annular valve seat as. Port 7% communicateswith bore portion 82 by way of passageway 88, and ports 66 and 68 areadapted to communicate with bore portion or valve chamber 84? by way ofpassages and 92. A threaded insert plug 91 having a restricted opening93 therein communicates passage 76 with a chamber 95 in bore portion 84.

A generally cup-shaped fluid control poppet valve 94 having a truncatedconical control portion 96 which is adapted to seat on the valve seat 86is slidably mounted in chamber as, being urged in a closing directionagainst seat 36 by a control spring 9 3 which abuts the valve at oneend, as shown, and which is held in position by a cup-shaped springretainer 1% having an opening M2 which vents chamber 819 to theatmosphere through port 74. Spring retainer 1% is of predeterminedlength and provides an annular abutment edge N4 which limits the maximummovement of valve 94 in an opening direction. A pin fit?) is mounted inthe housing 6% transversely of the outer end of retainer wt? holding theretainer in position. A pilot valve member is adapted to operate valve94 under certain conditions and is composed of a guide stem 1% receivedin here portion 84 and an abutment head flit; disposed in bore portion Oring seals are provided on both valve portions 94 and 1% to preventfluid leakage through opposite ends of the valve. It will be noted thatvalve portion res, MP8 is not integral with control valve 94, but is aseparate piece which abuts the end of the conical portion of the lattervalve.

It may be assumed that when pistons 2t and 22 move to the left as viewin FIGS. 1 and 2, they are moving with load assistance, that is, theweight of a load on fork 14 is urging the pistons to move toward theleft to advance forward tilting movement of mast 32, but when thepistons move to the right to tilt mast 12 rearwardly from any givenposition thereof they move with load resistance. The operation of thecircuit is as follows: It may be assumed that a load is to be depositedand that the mast is in a vertical or rearwardly inclined position. Tofacilitate deposit of the load, pistons 2'9 and 22 are required to moveleftwardly; however, since the pistons tend to move to the left withload assistance there is a tendency for cavitation to take place in therighthand ends of the cylinders, which tendency is avoided as will nowbe explained.

To cause the pistons to move to the left, the directional control valve32 is shifted to the right to locate the crossover portion 4% in thecenter of the valve in order to supply pressure fluid from pump 34 tothe head ends of cylinders 16 and 1th by way of lines 36, 46, t) and 52,the valve ports 62, 64 and 72. Pressure fluid increases in the head endsof the cylinders, but because valve 94 is held in pressure contact withvalve seat 86 by spring 93, fluid cannot flow from the rod ends of thecylinders prior to opening movement of valve 94, which then permits thecylinder rod ends to communicate with sump 449 by way of lines 54, 56,ports 66, 68, the valve opening at seat 86, bore portion 82, port ill,and lines 44 and 38 by way of the return cross-over channel portion 48.However, as long as poppet valve 94 is maintained by spring 98 inpositive sealing relation to seat 86, no communication between the rodends of the cylinders and the sump can occur through the aforementionedcircuit. In closed position, valve 94 blocks completely any flow offluid from the rod ends of the cylinders and the pistons remain inlocked positions. Forward tilting movement of mast 12 can therefore onlyoccure subsequent to a buildup in pressure in the head ends of thecylinders and in passage 76 sufiicient to actuate pilot member 108 tothe left to open poppet valve 96 against the force of spring 93 andtoward a maximum open position established when valve 94 abuts edge 104of spring retainer 1%.

During the period of pressure build-up prior to opening movement ofvalve 94, it is apparent that equal pressure build-up occurs in the rodends of the cylinders, and that not until valve 94 opens lines 54 and 56to line 44 through the valve and connecting passageways in the valvehousing does the mast begin to tilt forwardly. Throughout forwardtilting movement of the mast, positive pressure is maintained in thehead ends of the cylinders by valve 94 irrespective of the angle offorward tilt of the mast or the load on fork 14 which tends to actuatethe mast with load assistance under such conditions. Valve operates toprevent any action which would tend to cause cavitation in the head endsof the weaves nation.

cylinders, since valve member will in operation o en and close asrequired to maintain the predetermined pressure level in the head endsof the cylinders as fixed by spring 93. Thus, the pistons ill and 22 aredriven to the left always under positive pressure in the head ends ofthe cylinders even though they have a tendency to stove to the left withload assistance.

Now it may be asumed that the load has been deposited or placed on thefork and that the fork and mast is to be actuated in a reverse orrearward tilt direction. To accomplish this, valve 3.2 is shifted to theextreme left so as to place parallel channels 42 in the center of thevalve thereby supplying pressure fluid to line 44 from the pump, whileline 46 is connected to the sump. Pressure fluid in line is directedinto valve bore portion 82 and acts upon the exposed conical valveportion 95 whereby to actuate valve to the left against spring 93.Pressure fluid then flows through ports as and 63 into the rod ends ofthe cylinders to pivot mast 12 to the right against the resistancethereof to movement in said direction, while eiecting fluid from thehead ends of the cylinders to the sump through ports 62; and 64 andthrough lines and 33. When a desired rearward tilt position of the mastis established, direction control valve 32. is returned to its closedcenter position, as shown in FIG. 2, whereupon spring 98 closes valve 94and pistons 2d and 22 are sealably locked in said selected position.

in this regard, it will be noted that if the lift truck is beingmaneuvered around corners and the like, the load would tend to twist themast one way or the other if lines and 56 were connected to each other.For instance, if the latter lines were interconnected, a twisting forceon the mast tending to move the piston it) to the left and the piston 22to the right would cause fluid to flow from the rod end of cylinder 16to the rod end of cylinder 18, thus enabling the mast to sway or twist.However, upon fixing the rearward tilt position of the mast, valve 94returns immediately to its closed position and prevents communicationbetwen lines 54 and 56, thus fixing the tilted position of the mastwithout any tendency thereof to sway or twist regardless of thesubsequent maneuvers of the truck. a

Small opening 93' in plug 91 functions as a dashpot during closingmovement of valve 94 and restricts the rate of opening movement of valve94, thereby preventing valve chatter and effecting a smooth andcontrolled rate of valve opening and closing movements. Thisconstruction permits the valve 94 to engage seat 36 with a sof action,thus permitting the use of relatively soft material in the valve bodyand valve.

In FIG. 4 there is illustrated a modification of the structure of valve36 in which similar parts have been numbered the same as in FIG. 3, butwith a prime desig- Valve 30 of FIG. 4 is operable in a manner similarto that of valve 39 and is substitutable for valve 30 in the hydrauliccircuit shown in FIG. 2. In the valve construction shown in FIG. 4, apoppet valve 112 has a pilot extension 114 which is integral therewithand which extends into bore portions 82' and 84 in a manner similar tothe mounting of corresponding valves 94, 1% of valve assembly 36. Aswill be observed, the various ports and passageways in valve housing 6%are located similarly to the location thereof in valve housing 60 andare adapted to be connected to the same lines of the hydraulic circuitas are the corresponding ports of valve housing 6%. Passageway 76 isconnected to the bore portion 84 by the threaded plug insert 91 having asmall passageway 93' therein. Insert member 91 performs the same dashpotfunction in the FIG. 4 construction as described above in FIG. 3.Opposite end portions of valve member 112, 114 include circumferentialgrooves in which 0 rings are located, as shown, to seal the valve fromleakage flow through the ends thereof into spring chamber or passage 76.Spring 93 abuts valve 112 at its one end and abuts a spring retainer andvent plug 126 at its other end, plug 120 having a spring guide andretainer member 122 and a vent opening 124 extending therethrough to theatmosphere. The embodiment of the valve construction shown in FIG. 4functions in the hydraulic circuit of FIG. 2 in the same way as does thevalve of FIG. 3, but is somewhat less expensive to manufacture, and forthat reason is preferred.

Although only only two embodiments of the present invention have beendisclosd herein, modifications in the structure and relative arrangementof parts will be apparent to persons skilled in the art, and I do notintend that the invention be limited otherwise than by the scope andspirit of the claims appended.

I claim:

1. In a flow control system for a load-handling apparatus having aplurality of piston and cylinder units, the pistons of which areactuated away from one set of ends of the cylinders with load assistanceand actuated away from the opposite set of ends of said cylindersagainst load resistance, means for connecting either set of ends of saidcylinders with a source of fluid under pressure and for exhausting fluidfrom either set of ends of said cylinders in correlatedin-one-end-out-the-otherend manner, said means including a single valve,a valve seat, means biasing said valve into fluid sealing relation withsaid valve seat, said valve in said sealing relation blocking exhaustfrom said other set of ends and being responsive to the pressure in saidone set of ends to allow the exhaust of fluid from said other set ofends only after build up of a predetermined pressure in said one set ofends to prevent cavitation in said one set of ends.

2. A flow control system as claimed in claim 1 wherein said single valvecomprises two separate axially aligned elements, one of which is apoppet valve element for seating on said valve seat, and the other ofwhich is a pilot element in abutment with said poppet valve element andsubjected to pressure in said one set of ends for opening said poppetvalve element against said resilient means. I

3. A flow control system as claimed in claim 1 wherein said single valvecomprises a poppet element adapted to abut said valve seat in sealingrelation and an element extending from said poppet element responsive tofluid pressure in said one set of ends of said cylinders for actuatingsaid poppet element in an opening direction against said resilientmeans.

4. In a lift truck having a tiltable load handling upright and a pair ofcylinder and piston units connected to the upright for tilting theupright forwardly and rearwardly such that the pistons tend to tilt theupright forwardly with load assistance and tend to tilt the uprightrearwardly with load resistance, a fiow control system including conduitand valve means for directing pressure fluid simultaneously to eitherthe head or rod ends of said cylinders, the head and rod ends of saidcylinders having respective cross-over conduit connections, a poppetvalve in the rod end crossover connection for preventing communicationbetween said rod ends of said cylinders, a valve seat normally engagedby said poppet valve in fluid sealing relation, means biasing saidpoppet valve into said sealing relation, and a pilot extension of saidpoppet valve responsive to pressure in the head ends of said cylindersfor opening said poppet valve under predetermined fluid pressure in saidhead ends, said poppet valve and extension thereof comprising the solecylinder pressure responsive control valve in the system.

5. In a lift truck as claimed in claim 4, dashpot means operable forcontrolling the rate of opening and closing movements of the poppetvalve relative to the valve seat.

6. A flow control system as claimed in claim 1, wherein said valveconstitutes the only cylinder-pressure-responsive control valve in thesystem.

7. A flow control system as claimed in claim 1, wherein said pluralityof piston and cylinder units comprises a pair of such units, andconnection means for said opposite set of ends of the cylinders of saidpair of units, said valve being disposed in said connection means toprevent communication of the pair of cylinders therethrough beforeoccurrence of said predetermined pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,470,778 5/49Lankovski 91-420 2,800,110 7/57 Haarmeyer 91-420 3,022,773 2/62 Olson91-411 3,033,168 5/62 Ruhl 9l420 3,053,234 9/62 Chevreux 91--313,093,116 6/63 Rood 91420 FOREIGN PATENTS 1,119,615 9/59 Germany.

449,876 7/ 36 Great Britain.

FRED E. ENGELTHALER, Primary Examiner.

SAMUEL LEVINE, Examiner.

1. IN A FLOW CONTROL SYYSTEM FOR A LOAD-HANDLING APPARATUS HAVING APLURALITY OF PISTON AND CYLINDER UNITS, THE PISTONS OF WHICH AREACTUATED AWAY FROM ONE SET OF ENDS OF THE CYLINDERS WITH LOAD ASSISTANCEAND ACTUATED AWAY FROM THE OPPOSITE SET OF ENDS OF SAID CYLINDERSAGAINST LOAD RESISTANCE, MEANS FOR CONNECTING EITHER SET OF ENDS OF SAIDCYLINDERS WITH A SOURCE OF FLUID UNDER PRESSURE AND FOR EXHAUSTING FLUIDFROM EITHER SET OF ENDS OF SAID CYLINDERS IN CORRELATEDIN-ONE-END-OUT-THE-OTHEREND MANNER, SAID MEANS INCLUDING A SINGLE VALVE,A VALVE SEAT, MEANS BIASING AND VALVE INTO FLUID SEALING RELATION WITHSAID VALVE SEAT, SAID VALVE IN SAID SEALING RELATION BLOCKING EXHAUSTFROM SAID OTHER SET OF ENDS, AND BEING RESPONSIVE TO THE PRESSURE INSAID ONE SET OF ENDS TO ALLOW THE EXHAUST OF FLUID FROM SAID OTHER SETOF ENDS ONLY AFTER BUILD UP OF PREDETERMINED PRESSURE IN SAID ONE SET OFENS TO PREVENT CAVITATION IN SAID ONE SET OF ENDS.